1. Field of the Invention
The present invention relates to an improvement in an automotive lamp bulb.
2. Description of Background Art
Japanese Laid-Open Utility Model Application Serial No. 4-81349 entitled "Halogen Lamp Bulb" describes an example of a technique related to automotive lamp bulbs.
FIGS. 6a and 6b are diagrams of a background art process for manufacturing a conventional halogen lamp bulb. FIG. 6a corresponds to FIG. 5 in the aforementioned application, while FIG. 6b corresponds to FIG. 6, but different symbols are used.
In FIG. 6a, a support wire 102 equipped with a glass tube 101 is inserted into a sealed glass body 103, the air is exhausted, and the assembly is heated. In the process, the exhausted gas or a halogen gas passes through a cylindrical conduit 104.
FIG. 6b is a diagram of the completed assembly and depicts a state in which the tip has been sealed by being softened and closed up with the aid of two burners (shown in FIG. 6a).
In the background art device of FIG. 6a, the passage resistance of the cylindrical conduit 104 is considerable because the glass tube 101 is long. The reason is that the passage resistance is directly proportional to the length and inversely proportional to the square of the cross-sectional surface area of the passage.
In view of this proportionality, the clearance must be enlarged in order to lower the resistance. An enlarged clearance increases the diameter of the sealed glass body 103. Considerable time is needed to reduce the large-diameter sealed glass body 103 to the shape shown in FIG. 6b.
To obtain a uniform clearance, it is necessary to align the center of the support wire 102 with the center of the sealed glass body 103, and an advanced technique is needed to achieve such centering.
Specifically, the background art technique involves complex processing steps and entails high processing costs.
Another feature of the problem is that, because of the considerable length of the glass tube 101 in FIG. 6b, a projection length HI of the sealed glass body 103 is inevitably increased, contributing to the bulkiness of the halogen lamp bulb.